Following the rapid development of modern technology, microfluidic pump is widely applied in all kinds of hi-tech field, such as biomedical detection and inkjet printing. The so-called “microfluid driving system” may be further classified as the follows according to its function: micro jet, micro droplet, and microfluidic mixing. Currently, there are many methods by which fluid actuation through microchannels can be achieved, including the direct usage of micropump or thermal bubble pumping, both of which drive microfluid by direct contact. The former, i.e. micropump, is widely applied in biochip and the structure thereof can be further divided into mechanical micropump and electrode-powered micropump, wherein the fabrication of the mechanical micropump is mainly by using the micromachining technique to directly layout built-in movable parts on chips, such as an electrostatically driven diaphragm micropump, which was proposed in U.S. Pat. No. 5,529,465, wherein, the main body thereof comprises four layers of crystalline silicon structure, and the actuation of the pump is completed using the circulation and exchange generated by the intermittent electrostatic interaction between two layers structure that functions in cooperation with two pieces of single-direction passive check valve inside the fluid channel. In addition, U.S. Pat. No. 5,705,018 proposed another micropump having simpler structure, i.e. micromachined peristaltic pump, which is fabricated mainly by implanting pieces of flexible conductive strip sequentially and densely on the inner walls of the microchannels of the chip, thus, when voltage pulse passes over the top of the microchannel, staticelectricity will be generated to sequentially attract the conductive strips to move upwardly to thereby create a peristaltic phenomenon for the microchannel to push the fluid in the microchannel to move forwardly.
On the other hand, the electrode-powered micropump is a kind of non-mechanical micropump without any movable part to be laid out on the chip. Its operating principle may be roughly classified as: electroosmosis (EO), electrohydrodynamics (EHD), and electropulse (EP). For example, U.S. Pat. No. 5,632,876 proposed a combining application of EO and EHD, which is a pumping device in a microchannel mainly comprising two pairs of electrodes inserted into the microchannels of the chip, the pair of electrodes located in the middle are more close to each other and are deepened into the fluid in the microchannels, so that when high voltage is conducted, the two closer electrodes will generate current circuit using the fluid in between, in the meantime, the surrounding fluid will be brought along to move in counter direction of the current to thereby form an EHD pumping effect, that is, the two closer electrodes operated together will form an EHD pump, in addition, another pair of electrodes which is farther to each other touch the microchannel's wall only slightly, thus, when high voltage current is conducted through, the microchannel's wall will be electrically charged, such that the surfaces of the materials where the positive and negative electrodes are located are covered with negative and positive charges, the same time, if the fluid contains negative particles, then they will be attracted and permeate toward the negative electrode which is piled with positive charges, and in the meantime, the fluid will flow toward the negative electrode to form an EO pumping effect, that is, the pair of electrodes that are farther can operate together to form an EO pump. The foregoing U.S. patent applies the two effects, which are EHD and EO, capable of generating two streams flowing in counter directions, and by controlling the raise and fall of the two effects so as to enable the guidance and control technique for microfluid, such as propulsion, repulsion, and stagnation.
In addition, the bubble-based micropump is widely applied in the field of inkjet printing, wherein a voltage pulse is applied to the electric resistance so as to heat and vaporize the ink for generating bubbles in the ink box and further increase the pressure therein, such that the ink may be jetted out from the nozzle of the ink box, moreover, when the voltage pulse is disappeared, the bubbles will disappear subsequently, therefore, the jetting action of ink may be proceed repeatedly by controlling the voltage input into the electric resistance.
Although there are different principles and structures for actuating the aforementioned microfluid driving devices, they are all belonged to the type of driving by direct contact, that is, the fluid to be driven must be heated or be applied with electrodes of different magnitudes. Therefore, there are many limitations unavoidably imposed upon the kinds of fluids that can be used. For example, the microfluid driving device driven by electrodes is only suitable to be used in conductive fluids, but applying electrode in the bimedical detection process may damage the fluid itself that will have affect on the accuracy of the detection. In addition, since the thermal bubble-based micropump directly heats and vaporizes the ink itself, the ink used must have stable thermal property, low conductivity, and low chemical activity, which are the reasons why the price of the ink used in ink-jet machine is so high.